Chemical shifts of the protons within a methyl group in a saturated hydrocarbon. Slow methyl group rotation

Abstract

In the proton NMR spectrum of both (Bu^t)₃CH and (Bu^t)₃COH at –150 °C, one of the three separate signals for the methyl groups of a tert-butyl group appears as three singlets of equal intensity, with a greater than 1 ppm range of chemical shifts, showing that one methyl group is rotating slowly on the NMR timescale with a barrier to 120° rotation of 5.3 kcal mol^–1(1 cal = 4.184 J).